Obesity and weight gain are significant public health issues in the US and other Western countries, and are among the few breast cancer risk factors that are potentially modifiable throughout life. Although many epidemiologic studies have reported on associations with various body size measures, the few studies conducted in African-American and Hispanic women have produced inconsistent and inconclusive results. We propose to assess associations with a wide range of lifetime body size measures utilizing data from a large population-based case-control study conducted in the San Francisco Bay area from 1995-2003. Breast cancer cases aged 35-79 years were identified through the Greater Bay Area Cancer Registry, controls through random-digit dialing. Information on self-reported and measured body size was collected through in- person interviews for 2,258 cases (596 Whites, 543 African-Americans, and 1,119 Hispanics) and 2,706 controls (646 Whites, 598 African-Americans, 1,462 Hispanics). The aims of this project are to assess associations of premenopausal and postmenopausal breast cancer risk with both static and dynamic measures of body size during adulthood and adolescence. Using logistic regression, we will estimate multivariate adjusted odds ratios associated with 1) height, weight, body mass index (BMI) in each decade of life and during the reference year; 2) weight gain at different time periods in adulthood and adult weight range; 3) body shape and comparative weight in adolescence; and 4) waist and hip circumferences, and waist-to-hip ratio as measures of body fat distribution. Lastly, we will perform stratified analyses to assess the modifying effects of other factors, including use of hormone replacement therapy, age, time since menopause, family history of breast cancer, and estrogen and progesterone receptor status. We will also assess the potentially modifying effects of physical activity and caloric intake. Notable study strengths include the large sample size, multiethnic composition of study population, population-based study design, comprehensive assessment of lifetime body size measures through in-person interviews and measurements, and extensive data on other potentially confounding risk factors. This study will make an important contribution towards a better understanding of breast cancer etiology, and the role of body size in particular, in understudied populations such as African-Americans and Hispanics. [unreadable] [unreadable]